The present invention relates to a rotor blade for a turbine, where the rotor blade (1) has a cavity (10). Turbines of this type include wind turbines, ocean current turbines, and tidal current turbines.
At the base, i.e. at the connection to the turbine hub, the rotor blades are exposed to very high torques, which requires very large and expensive flanged connections, also in order to guarantee the necessary stiffness. Flange connections of this kind are known from WO 2010/084320 A2 or WO 2011/077454, for example. Thus, the contour of the blade must also be adapted to these geometrical dimensions and cannot be optimized for energy generation. In addition, there are blades or vanes that are cast or welded onto the hub, such as the ship's propeller in U.S. Pat. No. 3,310,116. In addition, WO 2002/42638 A1 shows a turbine blade with an internal cavity, where the blade is made up of two halves, and one half is provided with stays or ribs. There is no connection between the journal and these ribs.
The invention is thus characterized in that the rotor blade has a cavity and at least two ribs at its lower end, where a journal is provided for connecting to the hub of a turbine rotor that is inserted through an exactly fitting opening in the bottommost rib into the lower end of the rotor blade and reaches as far as the topmost rib, where it is inserted into a recess, and which is form-locked and/or force-locked with the ribs, where the journal has at least one cone or ledge and is connected to it with a rib in a force-locked connection. The blade thus has adequate stability, ever if the lower end has a smaller diameter, where the proportion of the total length of the rotor blade used for energy generation can be increased substantially. As a result of the firm connection between journal and rotor blade, torques can also be transferred effectively in addition to bending moments.
A favorable embodiment of the invention is characterized in that the blade is made of steel. The blade can be made much smaller as a result. It may be welded out of sheet steel, however the base can also he a casting should the situation arise.
A favorable development of the invention is characterized in that the journal is connected to at least one rib by means of at least one bolt disposed in axial direction, where it can also be connected to at least one rib by means of a bolt disposed in radial direction or a pin, respectively.
An alternative embodiment of the invention is characterized in that the journal has another cone or ledge inclined in the opposite direction to the first cone or ledge. As a result, the forces acting on the blade can be transferred favorably to the journal and, subsequently, to the hub.
If, preferably, a retaining ring is provided that can be joined in a form-locked connection to the other cone or ledge, the blade can be secured in place easily and the forces transferred.
A development according to the invention is characterized in that tie rods connected to at least one rib are provided. In this way, the fastening devices can be pre-assembled easily, resulting in shorter assembly times on site. It is especially favorable if the journal is joined to the at least two ribs in a force-locked connection by pre-stressing the tie rods.
As an alternative, the journal can end in a twin-fit with the at least two ribs, and be held in place in a form-locked and force-locked connection by means of a clamping ring.
The invention also relates to a turbine, especially a tidal current turbine with at least two, preferably three, rotor blades set up as described above. A stable rotor blade is needed especially for tidal current turbines, where the rotor blade according to the invention has the advantage of good conversion of energy within a very small space. Several blades may also be provided. The steel design, in particular, provides a compact and stable construction for tidal current turbines or run-of-river turbines.